Re: [PATCH 15/15] x86/percpu: Remove !CONFIG_X86_CX8 methods

Uros Bizjak
2025-12-14T09:38:49Z

On Sun, Dec 14, 2025 at 9:48 AM Ingo Molnar <mingo@kernel.org> wrote:
>
> From: Uros Bizjak <ubizjak@gmail.com>
>
> Adjust the constraints to the non-alternatives asm() statement.
>
> Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
> Signed-off-by: Ingo Molnar <mingo@kernel.org>
> Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: "Ahmed S . Darwish" <darwi@linutronix.de>
> Cc: Andrew Cooper <andrew.cooper3@citrix.com>
> Cc: Ard Biesheuvel <ardb@kernel.org>
> Cc: Arnd Bergmann <arnd@kernel.org>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: "H . Peter Anvin" <hpa@zytor.com>
> Cc: John Ogness <john.ogness@linutronix.de>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Link: https://lore.kernel.org/r/15696bb3-126b-ef71-f838-80e1e1c1b0aa@gmail.com
> ---
> arch/x86/include/asm/percpu.h | 25 ++++++++++---------------
> 1 file changed, 10 insertions(+), 15 deletions(-)
>
> diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
> index 725d0eff7acd..4c84ae0ea261 100644
> --- a/arch/x86/include/asm/percpu.h
> +++ b/arch/x86/include/asm/percpu.h
> @@ -335,13 +335,10 @@ do { \
> old__.var = _oval; \
> new__.var = _nval; \
> \
> - asm_inline qual ( \
> - ALTERNATIVE("call this_cpu_cmpxchg8b_emu", \
> - "cmpxchg8b " __percpu_arg([var]), X86_FEATURE_CX8) \
> - : ALT_OUTPUT_SP([var] "+m" (__my_cpu_var(_var)), \
> - "+a" (old__.low), "+d" (old__.high)) \
> - : "b" (new__.low), "c" (new__.high), \
> - "S" (&(_var)) \
> + asm qual ("cmpxchg8b " __percpu_arg([var]) \
> + : "+m" (__my_cpu_var(_var)), \

The above line should read:

: [var] "+m" (__my_cpu_var(_var)),

> + "+a" (old__.low), "+d" (old__.high) \
> + : "b" (new__.low), "c" (new__.high) \
> : "memory"); \
> \
> old__.var; \
> @@ -364,14 +361,12 @@ do { \
> old__.var = *_oval; \
> new__.var = _nval; \
> \
> - asm_inline qual ( \
> - ALTERNATIVE("call this_cpu_cmpxchg8b_emu", \
> - "cmpxchg8b " __percpu_arg([var]), X86_FEATURE_CX8) \
> - : ALT_OUTPUT_SP("=@ccz" (success), \
> - [var] "+m" (__my_cpu_var(_var)), \
> - "+a" (old__.low), "+d" (old__.high)) \
> - : "b" (new__.low), "c" (new__.high), \
> - "S" (&(_var)) \
> + asm qual ("cmpxchg8b " __percpu_arg([var]) \
> + CC_SET(z) \
> + : CC_OUT(z) (success), \

CC_SET() and CC_OUT() macros have been removed in the meantime [1], so
the last two lines should be changed to:

: "=@ccz" (success),

[1] https://lore.kernel.org/lkml/20250907183420.48569-1-ubizjak@gmail.com/

Uros.